The present relation is related to a filling apparatus for a rotary tablet press. When the term “tablet press” is used in the following, then the same relates generally to a rotary press which presses powder shaped material together into pressed articles. These have not always to be tablets.
The typical construction of a rotary press is such that a rotor driven by a drive motor contains a die plate with die bores, as well as guides for upper and lower punches, which are actuated by radial cams and compression rollers, in order to co-operate with the powder material in the die bores. With die bores, passage openings in the die plate are meant, which are formed either by die inserts or by simple bores in the die plate or in segments of the die plate, respectively. The filling of the die bores takes place with the aid of a suitable filling apparatus, which is stationarily associated to the perimeter of the die plate. The filling opening of a chamber of the filling apparatus is associated to the pitch circle of the die bores. When the die bores pass below the filling opening, they are consecutively filled with the powder shaped material. In this, the lower punch is in each case arranged in the inside of the die bore, and with its position it determines the volume of the material to be compressed which is taken up by the die bore.
Different constructions for filling apparatuses have become known. In principle, they differ in that whether they supply the compression material to the die bores solely by gravitation, or whether they have a suitable conveying—or agitating means, respectively, in order to supply compression material fed into the chamber of the filling device efficiently to the die bores.
Filling via gravitation (with a chamber feed shoe) transports the compression material gently to the die bores. The filling of the die bores takes place via falling down of the powder into the die bores caused by gravitation. From on a certain speed of the rotor, such a filling apparatus does no more work with the necessary filling constancy.
When there is an agitation device in the chamber of the filling device, the same conveys the compression material to the die bores by mechanical scooping. This principle works reliably even at high speeds of the die plate. Admittedly, the powder shaped compression material is strongly stressed by the shear forces occurring in the scooping. In addition, demixing or destruction of the compression material may take place. A further disadvantage may be the fluctuating course of the pressure in the flow of the compression material, which is caused by strong deflections in the interior of the filling apparatus. Further, the sumptuous cleaning is disadvantageous.
The present invention is based on the objective to provide a filling apparatus for a rotary tablet press, which works reliably even at high speeds, treats the compression material with care at the same time and is easy to clean.
In the present invention, one single filling wheel is mounted in the chamber, which is rotatable around a vertical axis. The chamber is circular in the region of the rotation of the filling wheel, and can be formed circularly even above the filling wheel. Yet, it is also possible to block up this region outside of the filling opening, in order to form only a narrow flow section.
On its perimeter, the filling wheel has plural wings, spaced apart in the perimeter direction, which sweep over the filling opening in the rotation of the filling wheel. The inlet opening is arranged preferably approximately centred with the axis or near to the axis of the filling wheel, in a distance to the same.
In the filling apparatus of the present invention, the advantages of conventional constructions are combined. There is a gently material supply to the die bores even at high speeds. In addition, the filling apparatus of the present invention can be cleaned easily. Through its simple construction and the small number of assembly parts, the filling apparatus of the present invention can be cleaned manually as well as automatically without greater expenditure. Through this, cleaning- and setup times at for instance product changes are shortened. Demixing of individual substances of the compression material is minimised. Any mechanical load is avoided in a great extent. Pressure variations on the flow path for the compression material are also minimised.
In the filling apparatus of the present invention, the compression material supplied from the topside to the filling wheel, centrally for instance, is directed towards the side, which can take place particularly efficiently when the upper side of the filling wheel is formed conically in particular, so that the compression material is directed radially towards the outside after entering in the filling chamber. For instance, an efficient deflection may be achieved even in that the upper side of the filling wheel is helical. By the way, the upper side may even be realised to be smooth, or it may have a suitable condition of the surface.
In one embodiment of the present invention, the filling opening is lengthened to a bow-shaped channel (pre-filling channel) in the bottom of the filling chamber, which is aligned to the pitch circle of the die bores and which extends beyond the filling chamber opposite to the rotational direction of the die plate. The pre-filling channel is preferably open at its end. The compression material is therefore carried into the individual die bores via a longer path, wherein the die bores which enter below the pre-filling channel are at first partly filled via a gravitational filling, until they are subsequently completely filled up below the filling chamber, up to the upper edge of the die plate.
Another embodiment of the present invention provides that the lower surface of the filling wheel, situated radially inside of the wings, runs approximately plane parallel to the bottom of the filling chamber, and that the lower surface has at least one preferably helical bridge. The bridge prevents that compression material intrudes into the gap between the filling wheel and the bottom of the filling chamber and affects the operation of the filling wheel, when it arrives at the driving shaft of the filling wheel.
According to a further embodiment of the present invention, the drive of the filling wheel takes place via a central shaft, which is guided through the bottom of the filling chamber. It is provided with a suitable drive motor.
The wings in the filling wheel of the present invention are finger-like and extend approximately up to the circular side wall of the filling chamber. The finger-like wings are significantly smaller in their width than the spacing of the wings from each other. Their length is such that they sweep essentially only the region of the die bores.
According to a further embodiment of the present invention, the casing of the filling device of the present invention constructionally consists essentially only of a bottom plate and a cover plate, which form the filling chamber together, wherein the cover plate is preferably conical.